In an oil refinery, an amine unit is a processing unit that removes acid gases from a hydrocarbon process flow. The primary acid gases to be removed are hydrogen sulfite and carbon dioxide. Acid gases are commonly removed by contacting the hydrocarbon stream with an aqueous organic amine such as monoethanolamine (MEA), diethanolamine (DEA), methyldiethanolamine (MDEA), diisopropanolamine (DIPA), diglycolamine (DGA) or triethanolamine (TEA) diluted in water as an amine solvent. The amine solvent reacts with the acid gases in an absorber, thereby removing them from the hydrocarbon stream. The amine-acid gas reaction is later reversed in a stripper, resulting in an acid gas stream and a reusable solvent stream.
In the treatment of light hydrocarbons (C1-C7) in an amine unit, emulsions of the hydrocarbon in the aqueous organic amine can form. In addition, droplets of the aqueous organic amine can become emulsified in the liquid hydrocarbon stream (a water-in-oil emulsion) contaminating downstream hydrocarbon processing units. The residence time of the aqueous organic amine stream in the absorber is not sufficient to allow resolution or breaking of such emulsions. When such light hydrocarbon-in-water emulsions reach the stripper, the light hydrocarbon can expand from a liquid to a vapor causing uncontrollable foaming. The formation of foam in the stripper unit is undesirable and can overwhelm the separation process in the stripper. Typical attempts to control foaming in the stripper include the use of antifoams (silicone and nonsilicones), increasing the aqueous amine stream temperature, installation of a flash drum, and/or installation of an inlet gas separator. While such methods exhibit some efficacy, they are usually only partially successful or are costly to implement.